Swift variable: The definition, benefits and how to use it

Swift is a popular programming language for Apple’s iOS devices. It was released in 2014. This language is perfectly suitable with Apple’s applications like iOS, macOS, watchOS, and tvOS. Furthermore, this Swift comes with the LLVM compiler framework, which is open-source. As a result, many iOS app developers choose Swift as their favorite programming language. Moreover, Swift also has some fantastic features for iOS developers. In the previous blogs, we have already mentioned a lot of useful information about Swift. So in this article, we will continue the series by providing swift variable. Numbers, text, buttons, and photos are examples of variables in your code. Every piece of data used by your app is saved as a variable or constant. So are you ready? Let’s start our blog. 

What are swift variables and Constants?

Let’s take a look at the following example:

Swift variable

You define an age variable of type Int on the first line, and then you set the value 42 to it.

The print() function is used on the second line to print the value of the variable age.

As a result, the value 42 appears on the output. 

The above example declared and initialized a variable age in swift variable. Therefore, you must first declare and initialize a variable before you can use it.

  • Declaration: Announcing a new variable
  • Initialization: An initial value of variable
Syntax for declaring and initializing in the previous example:
  • var – used to begin a new variable declaration.
  • age – the variable’s name
  • : – separates the variable’s name and type.
  • Int – the variable’s type (a type annotation) 
  • = –  used to assign values to variable
  • 42 – the variable’s value
Swift variable

Is it possible to modify the value of a variable? Yes, look at an example:

Swift variable

Here’s how it works:

  • Firstly, you have to create a variable called age and give it the value 42.
  • Secondly, you will use the assignment operator =. And then you modify the value to 999
  • Finally, you will print() the age value 

Does that make sense? That’s fantastic!

Swift variable is created with var, and constants are created using let in Swift. The difference between a variable and a constant is that a variable can be modified after it has been set. However, a constant cannot be modified once it has been set. The let keyword is used to declare a constant as the following example:

Swift variable

Keep in mind that after a constant has been initialized, you are not able to change it. An error will occur if you use this code:


The print() function can be used to print the value of a variable to the Console or a debug output window fast. It will appear in Xcode below the editor or in the output window above the Sandbox. Because it’s such a basic debugging tool, it’s often referred to as “poor man’s debugging.”

Also read: Update Xcode: The comprehensive guide to do it successfully

Variable and Constant Types in Swift

A type is assigned to each variable and constant. Different swift variable types can store various types of data. A value of one type cannot be assigned to a variable of another type. You can’t modify a type once it’s been set.

Consider the following example:

let name:String = “Bob”

The type of this constant name is String. You’re giving it the string literal “Bob” as a value. It’s the literal meaning of the word “Bob.” It’s a “string” because it’s simply text, or a string of characters.

So you can’t do it:

let name:String = 101

Why not? Because the value 101 is an integer number, not a string! Additionally, the constant is of type String. So you can’t assign it to a name. Moreover, String constants can only have strings assigned to them.

Furthermore, Swift is a strong-typed programming language, which means that each swift variable must have a type, which cannot be modified after it is declared. It’s also type-safe, which means the Swift programming language will prevent you from making mistakes like assigning 42 to a String variable.

In Swift, you can work with a variety of simple swift variable types, including:

  • Int for integer numbers. For example: 42
  • Double for decimal numbers.  For example: 3.1415
  • String for text. For example:  “Bob”
  • Bool for the boolean logic values true and false

With the Cocoa Touch SDK, you can work with a lot more types in iOS development, such as:

  • For buttons, see UIButton.
  • Use UIViewController for view controllers.
  • For an on-off switch, use UISwitch.
  • CLLocationManager is a program that receives GPS coordinates.

Inferring Types with Type Inference

Firstly, Type inference is extremely important. Because it increases productivity. But it also makes your code easier to read. Therefore, you don’t have to manually write as many types. So it saves time.

Another benefit is the Swift compiler, which converts your Swift code into ones and zeros. It can optimize the types of your swift variable without requiring you to change them manually.

For example, if the Swift compiler finds that you’re just working with positive integers, it might change the type of your variable from Int to UInt. Thereby saving memory.

For example:

So what is the type of value? For example, we’re using an Int and a Double to add an integer to a decimal-point value. Because inferring the type of value to Int would result in the loss of the fraction, Swift will infer the value to be of type Double.

Type inference used with any type, including functions that return a value, expressions, and closures. It’s especially useful for clearly coding closures!

Do you want to know the type of an inferred swift variable or constant? Press and hold the Option key when clicking on a variable in Xcode’s code editor. A gadget appears, informing you of the variable’s type.

Swift variable

Type inference can increase the time it takes to generate your app if you have a huge codebase (more than 15.000 lines of code). Swift also is difficult to infer a personality type. hen this happens, using a type annotation to declare specific kinds explicitly can help.

The type(of:) function can also be used to determine the type of a value during runtime. For example:

Further Reading

Above all, ArrowHiTech delivers you a lot of useful information about swift variables. Moreover, in case you need more information about Web/app development. So do not hesitate to contact us. We are experienced professionals in the field of  ECommerce, Web/mobile apps, CMS website development as well as Salesforce and Software Consultant & Development.